Abstract : For maritime applications like offshore foundations of wind turbines, durable sensors and sensor systems with low noise levels are needed which are well suited for the harsh environmental conditions. Additionally, the restricted offshore repair opportunities and therefore the urgent need for high reliability have to be taken into account. In order to monitor welded seams in these applications areas, sensor rings were tested and qualified. Sensors are positioned in a ring around the pipe. The area of the welded seam is investigated by ultrasonic waves. Especially the correct positioning of the damage demands for highly sophisticated processing algorithms which are able to reconstruct the damage reliably from the recorded signals. The present paper introduces a technique to localize cracks in cylindrical structures. The proposed technique is based on the use of elastic waves propagating in hollow cylinders The so-called guided waves are used in a variety of wave modes. Every wave mode induces a different interaction potential with a crack depending on frequency and elastic stress components. Using the Finite difference method, the time-dependent elastic problem is solved by the simulation software Wave3000Plus to determine well-suited wave modes and frequency domains for the interaction of waves with the expected cracks. Subsequently, measurements using a cylindrical test structure were performed to verify the simulation results. Varying wave modes provide differing main oscillation directions and require the usage of shear transducers and thickness crystal transducers. Furthermore, the synthetic superposition technique is approved by experiments on cracks with varying depth.